Alternatively, MBS fusion rules can be demonstrated by running the two protocols in reverse: starting from a closed island (last step in Fig. REF ), and going towards a fully open configuration. In this case, the system is initialized in a state with a well-defined parity of MBSs 2&3, evolving into a situation where MBSs 1&2 and 3&4 couple. In this case, the parity of MBSs 1&2 and 3&4 determine the supercurrent at the left and the right interface [1]}. This would allow measuring the outcome of the protocols through supercurrent measurements, which have to be performed faster than the system relaxation timescale.
